With internal combustion engines with supercharging, especially turbocharging, at low engine revolutions and thus with low mass throughflows in the exhaust system, what is referred as turbo lag occurs. In this operating range efficiency of the turbocharger is low and a relatively low torque of the internal combustion engine is produced at full throttle. The turbo lag can be reduced by scavenging the cylinder or the cylinders of the internal combustion engine.
During the scavenging fresh air is flushed through a cylinder of the internal combustion engine into its exhaust system. In this case, for operating points of the internal combustion engine in which scavenging is taking place, a degree of delivery—i.e. for a given capacity of the internal combustion engine a ratio of actual fresh air remaining in the cylinder after a change of charge to a theoretically possible filling of the cylinder with fresh air—can no longer be determined in a conventional manner.
It is in fact not known how much of the total air has passed through the cylinder and how much remains in the cylinder. For optimum or almost optimum operation of the internal combustion engine it is thus necessary to know a mass or a volume of scavenging air or to determine a trapping efficiency of the relevant cylinder which is a measure of how much fresh air from the scavenging air remains in the cylinder.
A mass or a volume of air which flows into the internal combustion engine can be detected by measurement, e.g. by means of an air mass meter. A mass or volume of air, which flows from an induction manifold of the internal combustion engine into the relevant cylinder, is mostly model-based and determined with the assistance of pressure sensors in the induction manifold for example.
However the air mass or air volume remaining in the cylinder after scavenging of the cylinder is relevant for torque generation of the internal combustion engine and thus also for formation of a mixture in the cylinder. The air mass remaining in the cylinder is modeled with the aid of the trapping efficiency (mostly designated by α) in order to compute the torque of the internal combustion engine and thus be able to control or regulate it. In addition the air mass or volume remaining in the relevant cylinder is used to compute a currently required fuel mass or volume.
In the prior art the trapping efficiency and/or the scavenging air mass or volume of the relevant cylinder of the internal combustion engine is determined by an exhaust gas analysis and/or an offline charging change calculation with low and high pressure indicating.